The present invention relates to a short-time arc welding system for welding elements, such as for example metal studs, on to components, such as for example metal sheets, with:                a welding head device which has means to move an element in relation to a component,        a feed unit to feed elements to be welded to the component, and        a control and energy device, with:                    a power supply device for supplying power to the welding head device;            a feed control device for controlling the feeding and the movement of an element relative to the component;            a safety switch for monitoring the safety functions of the welding system, which safety switch permits, in addition to an operating state ON, in which a welding operation or a series of welding operations is rendered possible, at least one further operating state STOP OPERATION, in which the output voltages of the power supply device and of the feed control device are at least blocked.                        
The invention further relates to a process for controlling such a welding system.
Such a short-time arc welding system and process for short-time arc welding are known generally by the term “stud welding”, for example from the brochure “Die neue TUCKER-Technologie. Bolzenschweiβen mit System!” [“New TUCKER technology. The stud welding system!”], published by Emhart TUCKER in September 1999.
The technology of stud welding is used in automotive engineering in particular, but not exclusively. Using this technology studs with or without a thread, nuts, eyes and other elements can be welded on to body panels. As a rule, the elements then serve as holding anchors for fastening, for example, interior trim elements to the vehicle body.
In the case of the above-cited stud welding according to TUCKER, initially an element is placed in a welding head. This can take place by means of an automatic feed device, for example by means of compressed air. The welding head then positions the element at the appropriate point on the component. Next a pre-welding current is switched on which flows through the stud and the component. The element is then raised in relation to the component, as a result of which an arc forms. The arc flow is selected such that initially contaminants, surface coatings such as zinc, oil or dry-film lubricants, etc. are burned off. The current then switches to a welding current. As a result of the high welding current the mutually opposing end faces of the element and component melt. The element is then lowered again on to the component so the mutual melts are mixed. The welding current is switched off when the element reaches the component and the arc short-circuits. The melt solidifies and the weld joint is complete. Here the element is raised and lowered in relation to the component in a more recent embodiment by means of an electric motor, in particular by means of a linear motor, which effects a controlled movement of the element.
For power supply and for controlling the welding operation a control and energy device is provided according to the above-mentioned brochure, which device has a power supply device for providing energy to the welding head device, as well as a feed control device for controlling the feeding of elements for welding by means of the feed unit and for controlling the drive of the feed control device for raising and lowering elements. The control and energy device further comprises a safety switch apparatus for monitoring the safety functions of the welding system which permits, in addition to an operating state ON, in which a welding operation or a series of welding operations is rendered possible, at least a further operating state STOP OPERATION, in which the output voltages of the power supply device and of the feed control device are at least blocked. This STOP OPERATION state renders a simplified, fresh start-up of the welding system after switching off possible.
Users of such a welding systems expect maintenance of the system to be as simple as possible for which purpose a fault detection or fault rectification is to be rendered possible in as simple a manner as possible, the ongoing production process being hindered as little as possible. In addition, by its nature such a welding system, which operates with welding currents of several hundred amps and more, must comply with substantial safety requirements.
The object of the invention is therefore to indicate an improved short-time arc welding system or an improved process for controlling such a system, rendering possible simplified maintenance of the system and simplified fault diagnosis, simultaneously complying with a high safety standard. This object is achieved in the case of a short-time arc welding system of the type mentioned at the outset by means which permit the selective activation of individual components of the system in the operating state STOP OPERATION wherein means to secure from selective activation by unauthorized persons are provided.
The object of the invention is further achieved by means of a process for controlling a system of short-time arc welding elements, such as for example metal studs, on to metal components, such as for example metal sheets, in which process the elements are welded to the component by a welding head device being moved in relation to the component by means of an arc with the following steps:                monitoring the system for a stop command;        determining whether the stop command is a command for STOP OPERATION only to partially shutdown the system;        if the stop command is a command for STOP OPERATION, delaying a power supply device for the welding head device and a feed control device for controlling the feeding of elements and controlling the movement of an element relative to the component, and at least subsequently blocking the output voltages of the power supply device and of the feed control device;        monitoring whether a switch secured from unauthorised actuation emits a switching signal for an operating mode MANUAL OPERATION;        monitoring whether a permission sensor emits a sampling signal; and        if the signal for MANUAL OPERATION is received and the sampling signal of the permission sensor is received, enabling certain functions of the welding system with simultaneous blocking of the output voltage of the power supply device.The object of the invention is achieved entirely in this manner.        
According to the invention the selective activation of individual components of the system is now rendered possible, a high safety standard being guaranteed simultaneously by the means for securing from selective activation by unauthorised persons. In any case, even with selective activation of individual functions of the welding system it is also guaranteed that the power supply device cannot deliver any output voltage because such output voltage is either blocked or is disconnected from the mains supply. In this manner it is guaranteed that welding processes cannot be activated in any instance during maintenance or diagnostic work. Maintenance and/or diagnostic work is substantially facilitated because the entire system does not have to be examined in the shutdown state, and individual functions of the welding system can be checked specifically.
In a suitable development of the invention a main switch is provided which is designed as an EMERGENCY STOP switch on activation of which the control and energy device is directly disconnected from the mains supply and is shut down. In this manner the EMERGENCY STOP switch necessitated in any case pursuant to the relevant regulations can simultaneously be used as a main switch by which means the construction is simplified.
According to a further development of the invention, at least the output voltages of the power supply device and of the feed control device are blocked in the operating mode STOP OPERATION, an operating mode selector being provided which is secured from unauthorised use, said selector being coupled to the safety switch in order to facilitate selective activation of individual components of the system in the operating state STOP OPERATION. In this manner a high safety standard is maintained.
In a further development of the invention the power supply device comprises a constant-current source the output voltage of which can be blocked via a pulse blocker switch. In this manner the pulse blocker switch which is normally present in any case in such welding systems, can be used to block the output voltage of the power supply device safely if during partial stop operation for maintenance work individual components of the welding system require selective activation. In addition the pulse blocker switch can be used for specific delay of the welding operation the welding process is to be halted.
In an expedient development of the invention the control and energy device has a control device for controlling the welding system and an input device for inputting operating commands.
In further advantageous development of the invention, the welding head device can be coupled with an external operator control via which a welding operation can be activated in the operating state ON. In this manner the welding head device can sensibly be integrated into the external control of a production process.
In a further advantageous development of the invention the control and energy device has a customer interface which can be coupled with the external operator control preferably via a bus. The coupling of the control and energy device to an external control system is hereby rendered possible in a particularly simple manner.
According to a further development of the invention, the operating mode selector permits switching between the operating modes AUTOMATIC, wherein the welding operation can be activated via external operator control in the operating state ON, and MANUAL OPERATION wherein at least the output voltage of the power supply device is blocked.
Here preferably the operating mode selector is coupled with a permission sensor which allows activation of selected functions of the welding system in the operating mode MANUAL OPERATION on manual activation and simultaneous actuation of the external operator control in two-hand operation.
As a result of these measures it is guaranteed that activation of certain functions of the welding system is only possible in two-hand operation, because to activate an operation the user has to actuate the permission sensor with one hand and has to grip the external operator control with the other hand. In this manner high safety is guaranteed from manual contact with the welding head or the feed device with partial cancellation of the STOP OPERATION, the permission sensor in the operating mode MANUAL OPERATION being capable, for example, of feeding elements by means of the feed unit and activating a drive for the welding head device to raise and lower elements. These are the most important diagnostic tasks which can be permitted in the case of faults without impairment of safety.
According to a further development of the invention, the safety switch apparatus has a further operating state OPERATOR'S SAFETY on activation of which the power supply device and the feed control device are delayed and disconnected from the mains supply, while the control device and input device remain on protective low voltage and the customer interface is supplied with voltage, a manual cancellation of the operating state OPERATOR'S SAFETY leading to resumption of the operating state ON after a time delay. By means of this measure the control and energy device can be shut down safely in the event of a necessary halt without causing complications in an ongoing welding process, for example if a user opens a door of the control and energy device, while simultaneously a simplified, new start-up is possible.
In a corresponding manner preferably in the operating state STOP OPERATION the output voltage of the power supply device is blocked and the feed control device is delayed and disconnected from the mains supply, the control device and input device remaining on protective low voltage and the customer interface being supplied with power, a manual cancellation of the state STOP OPERATION immediately leading to resumption of the operating state ON. The operating state STOP OPERATION thus essentially corresponds to the operating state OPERATOR'S SAFETY, but with reduced effect, because the power supply device is not disconnected from the mains supply rather the output voltage thereof is only blocked, whereupon after manual cancellation of the STOP OPERATION state the standby state is immediately resumed.
In an advantageous development of the invention the safety switch has connections for coupling to an external control system, for example to the external operator control for transmitting safety functions. Here the connections are preferably designed with safe technology with one or more channels or are designed as a bus and are preferably designed for the transmission and monitoring of commands for STOP OPERATION and OPERATOR'S SAFETY.
In this manner safety functions can be transmitted with safe technology in the case of the external operator control or an external control system into which the external operator control is integrated, wherein for example an external EMERGENCY STOP request leads only to the state OPERATOR'S SAFETY in the case of the control and energy device. The safety switch is designed with safe technology in a preferred development of the invention. In this manner an extremely high safety standard is guaranteed in respect of the hardware.
It is understood that the features cited hereinbefore and those features to be described hereinafter can be used not only in the combination indicated but also in other combinations or in isolation, without going beyond the scope of the invention.